P0407
Exhaust Gas Recirculation Sensor B Circuit LowP0407 is a generic OBD-II powertrain diagnostic trouble code: Exhaust Gas Recirculation Sensor B Circuit Low. It is logged by the engine control unit when the egr monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0407 means
P0407 — "Exhaust Gas Recirculation (EGR) Sensor \"B\" Circuit Low" — is stored when the ECM detects that the voltage signal from the secondary EGR valve position sensor falls below the minimum threshold of the expected operating range. Sensor \"B\" is the second potentiometric position-feedback element on EGR valves equipped with dual-sensor feedback — an architecture found on a number of Toyota 1GD-FTV and 2GD-FTV diesel engines, Ford Duratorq Puma variants, Mazda SH-VPTS diesels, and some Bosch high-pressure EGR valves used on European diesel applications. The dual-sensor design provides the ECM with redundant position feedback, allowing it to cross-check the two signals for plausibility and to continue closed-loop EGR control even if one sensor degrades.
P0407 is, in electrical terms, the sensor \"B\" counterpart to P0405: the signal from sensor B is below the acceptable lower bound (typically below ~0.3–0.5V), indicating a short to ground on the signal wire, an open sensor ground, a broken signal wire, or an internally failed sensor B element. Because sensor \"A\" may continue operating normally when P0407 is set, the engine may not exhibit obvious drivability complaints — the ECM can often substitute sensor A feedback to maintain approximate EGR control. However, the PCM will typically flag a fault and illuminate the MIL to prompt inspection.
On vehicles where P0407 appears alongside P0405, both position sensors on the EGR valve are reading low simultaneously, which more strongly suggests a shared electrical fault (common ground, common reference, or connector-level fault) rather than two simultaneous independent sensor failures. Heavy carbon deposits that seize the valve in the closed position can cause both sensors to report sustained low readings and set both codes.
Common causes
Most-frequently reported root causes when P0407 is logged.
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1
Failed EGR valve position sensor \"B\" — internal potentiometer element degradation or burnout causing near-zero output voltage.
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2
Short to ground on the sensor \"B\" signal wire — chafed or pinched harness conductor contacting the engine block or chassis.
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3
Open circuit in the sensor \"B\" ground path — broken or corroded ground wire pulling the signal voltage low.
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4
Loss of 5V reference voltage shared between sensor A and sensor B — a common-reference fault (blown fuse, short on sibling circuit) collapses both sensor outputs.
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5
Corroded, water-damaged, or loosely-seated dual-sensor EGR connector degrading the sensor \"B\" signal pin.
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6
Heavy carbon soot accumulation in the EGR valve mechanically seizing the pintle at the closed (low-voltage) position.
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7
EGR vacuum solenoid or actuator failure preventing valve movement while both sensors report the stuck closed position.
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8
PCM input fault on the sensor \"B\" channel (uncommon — only after wiring and sensor are confirmed serviceable).
Symptoms drivers notice
How to diagnose P0407
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and retrieve all stored and pending codes; specifically check whether P0405 is also present — simultaneous sensor A and sensor B low codes point toward a shared electrical fault.
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2
With the ignition on and engine off, monitor live sensor \"B\" voltage — a reading below 0.3V confirms the low-circuit condition; compare it against live sensor \"A\" voltage to assess the scale of the fault.
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3
Inspect the EGR dual-sensor connector and wiring harness for corrosion, bent or pushed-back pins, chafed insulation, and oil or soot contamination.
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4
Verify 5V reference voltage at the sensor connector — if reference is absent, trace back to the shared ECM reference circuit (a fault there will cause both sensor A and sensor B to read low).
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5
Check sensor \"B\" ground path continuity from the connector ground pin to chassis ground — high resistance confirms an open ground fault.
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6
Disconnect the sensor connector and measure the \"B\" potentiometer resistance from signal pin to ground pin across the expected valve travel range; an erratic or open-circuit reading confirms a failed sensor element.
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7
Test EGR valve mechanical movement; if the valve is carbon-locked, clean or replace the valve assembly and retest sensor voltages.
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8
Perform circuit resistance measurements: sensor \"B\" signal circuit should measure approximately 1 kΩ ± 10% on most dual-sensor EGR designs; deviations outside this range indicate harness or sensor faults.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Which vehicles are most likely to set P0407?
P0407 is most common on vehicles equipped with dual-position-sensor EGR valves: Toyota Land Cruiser, Hilux, and HiAce models with the 1GD-FTV or 2GD-FTV diesel engine; some Ford Transit and Ranger diesel applications; Mazda BT-50 and CX-5 diesels; and European diesel platforms using Bosch high-pressure EGR valves with integrated dual-sensor feedback. On single-sensor EGR systems, sensor \"B\" codes are not in the PCM calibration and will not appear.
What is the difference between P0407 and P0405?
Both codes indicate a low-voltage condition on an EGR position sensor signal circuit, and both share the same set of electrical causes. The distinction is which sensor on the EGR valve is affected: \"A\" is the primary or first sensor (P0405), \"B\" is the secondary or second sensor (P0407). On dual-sensor valves, the ECM uses both for cross-check validation; losing sensor B alone is less immediately critical than losing sensor A, because the ECM can often maintain approximate control from sensor A.
Can I drive with P0407 active?
The vehicle is typically drivable for short distances. On dual-sensor EGR systems, the ECM often continues closed-loop EGR control using sensor A as a substitute, so the driver may notice little change in performance. However, continued operation risks worsening the fault (especially if the root cause is carbon buildup or moisture in the connector) and will result in a failed emissions test. Repairs should be completed promptly.
P0405 and P0407 appeared at the same time. Does that mean the whole EGR valve needs replacing?
Not necessarily. When both sensor A (P0405) and sensor B (P0407) show low codes simultaneously, the most likely cause is a shared electrical fault — a common ground fault, a failed 5V reference supply, or a damaged multi-sensor connector affecting both signal paths. Check the connector and reference circuit first. If both sensors are confirmed electrically healthy but the valve is carbon-seized in the closed position, the valve assembly (sensors included) will need replacement.
Disabling P0407 in software
RaceTune can permanently disable P0407 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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